Question

A small airplane flies 1050 miles with an average speed of 300 miles per hour. 1.75 hours after the plane leaves, a Boeing 747 leaves from the same point. Both planes arrive at the same time; what was the average speed of 747?

Answer 1

We need to finish writing out the problem using what we know about the distance both planes traveled.

Plane 1 - 1050 miles - 300 mph - ? time

Plane 2 - 1050 miles - same time as Plane 1 less 1.75 hours.

Let's fill in the gaps.

Plane 1 - ? time 1050/300 = 3.5 hours

Plane 2 - ? time Take 3.5 hours and subtract 1.75 = 1.75 hours

Now we figure the speed of plane 2

1050/1.75 = 600 miles an hour

Another quick way was to note that 1.75 was half of 3.5 hours so the speed was 2x as fast!